Most conventional motorized vehicles include a powertrain that has a power source, such as an internal combustion engine, connected to a multi-speed power transmission that is adapted to manipulate and transmit power from the engine to a final drive (e.g., driveshaft, differential, and wheels) for propelling the vehicle. Traditional powertrains having an automatic transmission generally include a hydrodynamic input device, such as a torque converter, positioned between the engine and the transmission. The torque converter is a hydrokinetic fluid coupling employed predominantly to allow the engine to run without stalling when the vehicle wheels and transmission gears come to a stop, and to provide torque multiplication in the lower speed range of the engine.
The hydrodynamic torque converter essentially consists of an impeller member, a bladed turbine, and a fluid stator. The impeller member, also referred to in the art as the torque converter pump, is secured to an annular shell member that is adapted to drivingly connect the impeller to the engine crankshaft. The bladed turbine is traditionally connected to an input shaft of the automatic transmission through a turbine hub. The stator mechanism, disposed between the fluid inlet of the impeller and the fluid outlet of the turbine, redirects fluid from the turbine to the impeller to improve flow efficiency and increase torque multiplication of the torque converter. The impeller accelerates hydraulic fluid for passage to the turbine; the turbine in turn converts the kinetic energy from the impeller into mechanical energy, which is transmitted to the transmission input shaft.
In many torque converter assemblies, the annular shell member and the bladed turbine cooperate to form a chamber for housing a torque converter clutch, also referred to in the art as a lock-up clutch. The torque converter clutch (or “TCC”) is operated to provide a bypass mechanism, allowing the engine to circumvent the torque converter and transmit power directly to the transmission.
Many conventional TCC's incorporate two clutch structures disposed in serial drive relationship—a friction clutch and a viscous shear clutch. The friction clutch includes a pressure plate having a friction surface disposed thereon and biased out of engagement with the annular shell member by a spring member. The pressure plate responds to a hydraulic actuator imparting fluid pressure thereto, urging the friction surface against the annular shell member, effectively locking the impeller to the turbine.
The TCC may be fully engaged (completely locked-up) or partially engaged (selectively “slip” in a controllable manner.) In the partially engaged state, the TCC friction surface is allowed to slip along the contact surface of the annular shell member; frictional heat is generated by the TCC when partially engaged due to this slipping phenomenon. Traditionally, heat generated by the TCC is attenuated by hydraulic fluid, such as automatic transmission fluid (ATF), inside the torque converter housing, which is circulated out of the assembly to a heat sink and thereafter recycled.
The circulation of ATF keeps the transmission within the normal operating temperature range. Oil routing through the transmission and torque converter assembly have been designed for most cooling purposes. In heavy-duty and/or high performance vehicles, an auxiliary transmission oil cooler assembly may be used. Mounted in front of the radiator, it serves as a cooler for the ATF so transmission temperatures do not exceed the required operating range. However, such additional componentry leads to increased costs and added vehicle weight (which leads to decreased fuel economy.)